The present invention is directed to methods and apparatus for harvesting and implanting bone plugs. The invention has particular utility in repairing damaged bone tissue, such as articular cartilage and underlying subchondral cancellous bone in the knee and other weight-bearing joints.
Weight-bearing joints, such as the knee, are particularly susceptible to injuries caused by friction between opposing bone surfaces. To understand the causes of such injuries, it is first necessary to understand the anatomy of a such a joint. In this regard, FIG. 1 illustrates knee joint 10. As shown in FIG. 1, knee joint 10 connects femur 12 to tibia 14 and fibula 18 via connective tissue 15 and 17 Interposed between opposing surfaces of femur 12 and tibia 14 are lateral and medial meniscus cartilages 21 and 23, respectively. Condyles 22 at distal end 11 of femur 12 are supported by meniscus cartilages 21 and 23 on proximal end 13 of tibia 14. Normally, distal end 11 of femur 12, including condyles 22, is covered by layer 28 of cartilaginous material which is about 5 mm thick. This layer 28 is called the articular cartilage.
Articular cartilage 28 forms a generally resilient pad which is fixed to distal surface 11 of femur 12 in order to protect femur 12 from wear and mechanical shock. When lubricated by fluid in knee joint 10, articular cartilage 28 provides a surface which is readily slidable on the underlying surfaces of meniscus cartilages 21 and 23 or on proximal surface 13 of tibia 14 if one or both of meniscus cartilages 21 and 23 is partially or totally absent. Problems arise, however, if articular cartilage 28 becomes injured due to excessive near. For example, articular cartilage 28 can become torn or thin, or holes can develop therein. As a result of such injuries, osteochondritis and/or arthritis can develop, making movement of the joint painful In extreme cases, these conditions can result in disability if not treated.
Injuries of the foregoing type can be treated by replacing the joint, or portions thereof, with artificial materials. In some cases, however, it is possible to treat the injury by replacing only the bone tissue (i.e., the articular cartilage and/or underlying bone) at the site of the injury with a graft, or plug, from a healthy site. This option is preferable for a number of reasons. For example, surgery to transplant a bone plug is less invasive than that required for a joint replacement. In fact, bone plug transplant surgery is typically performed arthroscopically. Moreover, transplanting bone plugs leads to fewer post-operative complications, a shorter rehabilitation period, and better results overall, since it actually leaves patients with their original joint intact.
Surgical techniques for transplanting bone plugs typically involve removing the damaged bone tissue by drilling or cutting a hole at the site of the damage, and plugging this hole with a bone plug extracted from healthy bone tissue in the patient""s body. This healthy tissue is generally extracted from non-load-bearing joints or surfaces in order to minimize patient substantial discomfort.
Surgical instruments are currently available which may be used to harvest or extract a bone plug from a donor site and, then, to implant it into a pre-formed hole at a recipient site. A conventional harvesting instrument typically includes a tube having a cutting edge at the distal end. To extract a plug, the instrument is driven into the bone at the donor site and then removed, taking with it a plug of healthy bone tissue.
The conventional instruments for harvesting bone plugs described above suffer from several drawbacks. For example, it is difficult to regulate the size (i.e., the length) of bone plugs extracted by them. Moreover, the bone plug tissue is sometimes unduly damaged or traumatized by excessive forces exerted during extraction or implantation.
Conventional instruments for implanting bone plugs also suffer from drawbacks. Generally, it is difficult to gauge the exact depth of plug insertion and, thus, to avoid slight protrusions or cavities. This problem is compounded in those instances where the donor and recipient sites do not have matching surface contours.
Thus, there exists a need for a bone plug harvesting apparatus which can be more easily used to remove plugs of bone, and which enables a surgeon to regulate the size of the bone plug being removed. In addition, there exists a need for a bone plug implantation apparatus which permits the plug to be implanted level and in proper alignment with the surrounding bone.
In view of the foregoing, an object of the invention is to provide improved methods and apparatus for harvesting and implanting bone plugs.
Another object is to provide such methods and apparatus as to permit the size of extracted plugs to be better regulated.
Still another object of the invention is to provide such methods and apparatus as to minimize trauma to the transplanted plugs.
Still another object is to provide such methods and apparatus as to facilitate accurate placement of bone plugs during implantation.
Yet still another object is to provide such methods and apparatus as to facilitate implantation in instances where the plugs or recipient sites have uneven contours.
The present invention addresses the foregoing needs by providing, in one aspect, a bone plug implantation apparatus having a translucent and, preferably, a transparent or clear tip, through which the bone plug can be viewed during implantation. Unlike the prior art, inclusion of such a tip permits the surgeon to view the bone plug during implantation, thereby facilitating better placement, alignment and insertion of the plug into the donor site.
According to further aspects of the invention, the apparatus includes a xe2x80x9charvestingxe2x80x9d tube which can be used to harvest the plug and which is used to hold the bone plug prior to implanting. The apparatus can also include a push rod that forces the bone plug into a pre-formed hole at the transplant site. The harvesting tube can include an aperture or recessed inner wall that reduces friction on the plug during implantation (and harvesting) and that, thereby, reduces undesirable compression of the plug.
According to further aspects of the invention, the tip has an inner diameter substantially equal to that of the hole into which the bone plug is transplanted. An outer diameter of the tip, however, can be greater than that of the hole. This larger outer diameter forms a shoulder upon which the tip can rest during implantation. The tip also covers the distal end of the harvesting tube and, hence, minimizes the damage that it might otherwise cause at the transplant site.
In still further aspects of the invention, the tip is rotatable relative to the harvesting tube. This facilitates rotation of the bone plug relative to the transplant site, e.g. so that their respective surfaces can be aligned and otherwise better fitted
According to still another aspect, the present invention provides an apparatus for harvesting plugs from bone tissue. The apparatus includes a harvesting tube, as described above, to which a cutting sheath is fitted. The sheath, which includes a cutting edge and a cutting tooth, can include markings on its outer surface so that the depth of insertionxe2x80x94and, therefore, the length of the bone plugxe2x80x94can be determined during harvesting. The harvesting tube can likewise include markings on its outer surface, e.g., adjacent the aforementioned window, so that the position and length of the plus can be more accurately determined after harvesting.
According to still another aspect, the present invention provides a method of transplanting a bone plug from a donor site to a recipient size. The method includes harvesting the bone plug from the donor site utilizing a bone plug harvesting apparatus as described above. The harvesting tube of the harvesting apparatus is fitted with a tip as described above to form a bone plug implantation apparatus, also as described above. The tip of the implantation apparatus is placed over a pre-formed hole at the recipient site and the bone plug is forced from the tube, through the transparent tip, and into the pre-formed hole. In related aspects of the invention, the tip is rotated prior to implantation to assure a better fit.
Still further aspects of the invention provide a drill guide for use in bone plug removal and replacement. The guide comprises a tip and a harvesting tube as described above. A drill bit is guided through the assembled tube/tip and is used to form a hole at the recipient site. Use of such an assembly as a drill guide can improve the integrity of the transplant, e.g., if the same (or similar) tube and tip are subsequently used during implantation of the plug.